1

Many years ago, I've noticed that one without requirements of any 5V devices like USBs, he/she can completely bypass the power input circuit and the regulator. Feeding Pi Model A with power from v3.3 GPIO pin, and shorts 5v with 3.3v can be a practical solution.

I knew it should be proceed with caution since there was no protection, e.g. feed 5v to 3.3v could destroy it. I also found some nice measurements for it.

However, time passes and it's 2016 now. I do not know if the circuitry within Pi 2 or Pi 3 has been changed and made this approach insane. I wonder if it could fry some parts like the regulator.

Can I still power newer Pis (2/3) from 3.3v without any issues?

2

No. The SOC actually requires other voltages (especially 1.8V which runs most of the Pi). These are all derived internally from the 5V supply with a couple of switch mode regulators.

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  • Sorry for digging this up, but it sounds like your answer conflicts with the answer from @joan under which corresponds to what I have read on several locations (and Joan seems to be a quite trusted member too, so I am curious of what he means). What do you mean with No here? That it will not work at all, or that specific things will not work? – Zorglub29 Feb 28 at 9:00
  • @Zorglub29 Joan and I are in agreement - i.e. we both state the Pi can ONLY be powered through the 5V pin. The Pi will run on much less than 5V (although I doubt 3.3V) the SoC runs on 1.8/1.2V. The Foundation states "Under no circumstances should a power source be connected to the 3.3V pins." See Raspberry Pi Power Limitations This definitely would NOT work with current models. Joan is a brilliant programmer, I am an electrical engineer. – Milliways Feb 28 at 10:08
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Interesting, as I'm trying to do the same thing.

I was aware of folks running Pi from a single FePO4 as these are between 3.2 and 3.3V normally anyway, and charging the cell in use by using a boost regulator running from a single crystal solar cell 0.7V 1A

One interesting modification, regenerate the 5V supply by using an isolated gate supply running off the 3.2 as the regulator will only use what it needs. It could also do double duty charging the battery from solar. Add a graceful shut down (tm) using a MN1381C set to Vmin for the cell being used so that when the battery gets too low the Pi saves its status and shuts down to preserve onboard SD. When battery is fully recharged it turns back on.

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-1

You can power the Pi with 3V3 provided you put the 3V3 into the 5V pin (i.e. don't short the 3V3 and 5V pins, connect your 3V3 power supply to pin 2 or 4).

The Pi itself will work quite happily.

Of course peripherals such as HDMI and USB which need 5V are unlikely to work.

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  • 1
    Have you actually tested that? :) – Zorglub29 Aug 24 at 8:08
  • 1
    It works for the Pi models available at the time of the answer. I haven't tried later models of Pi. – joan Aug 24 at 8:57
  • So it should work with Pi 2 B for example, but not tested with the Pi Zero? – Zorglub29 Aug 24 at 9:01

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